In order for electronic devices, such as a vehicle navigation system or personal digital assistant (PDA), to provide global positioning services, a navigation device with a global positioning system (GPS) has to be perform signal transmission (if any), reception and processing, which allows determination of the coordinates of the current location of such a device. GPS utilizes twenty-four artificial satellites circling in six different orbits above the earth to continuously transmit GPS signals. If the navigation device is able to receive GPS signals transmitted by at least three satellites, then its current longitude, latitude and elevation, can be determined and its velocity and traveling direction can be computed with respect to a prior reading.
Additionally, when using the above navigation device to receive GPS signals, reception is sensitive to the external environment (such as weather and the surrounding terrain and buildings). For example, if the weather is rainy with heavy clouds in the sky, the amount of free electrons in the clouds is large, which may interfere with the GPS signals, such that the GPS signal strength received by the navigation device is too low to perform a proper reading. Also, if the navigation device is used in a tunnel or underground passage, the navigation device may not be able to receive GPS signals from the satellites well. However, in such situations, the GPS module inside the navigation device would not stop operating even if no sufficient GPS signals are received, which wastes power.
In order to solve the above problem, one current approach is to provide a button for turning on/off the power of the navigation device, such that the operating power of the navigation device is controlled by a user upon determining the strength of the signals received by the navigation device. However, such a solution requires the user to check for the signal strength from time to time while possibly engaging in some other activities (e.g. driving a car), in order to know whether to turn off the operating power of the navigation device when the GPS signal strength is too low. This approach is not very convenient and even poses danger if the user is driving. Moreover, since the signal strength is manually checked, periods with low signal strength may be overlooked, such that wasteful power consumption is not completely avoided.
Therefore, there is a need for a power control system and method for the same that prolongs the operating time of the satellite navigation device by saving power and eliminating the need for manual operation.